Narrow generated JSON types

[tylergannon]

Summary

• emit generated JsonValue aliases for PostgreSQL json/jsonb instead of any
• wrap scalar JSON parameters with sql.json(...), preserving SQL NULL for nullable params
• fail on missing sqlc type metadata instead of falling back to any
• extend examples and docs for nullable/non-nullable jsonb

Verification

• just test
• just lint
• npx tsc --noEmit (examples/node-postgres)
• bunx tsc --noEmit (examples/bun-postgres)

CI also rebuilds the WASM plugin and verifies generated examples with sqlc diff.

[tylergannon]

Closing: opened against the wrong repository. The intended target is tylergannon/sqlc-gen-typescript.